January 8, 2019

Glossary

Broad-Acre

Climate Control

Extreme climate control is a greenhouse with heaters, ventilation fans, and moveable screens in the roof. Porous canopies can achieve many of the same effects though to a lesser level, depending on the fabrics and supporting structures utilised.

Distorting Net

Nets are made in a diagonal mesh pattern (see fabrics). By pulling on the end of a panel, the diamond gets narrower and longer, so the panel also gets narrower and longer. Distortions of up to 15% are easily achieved when required.

Erosion Control

Erosion from wind is dramatically affected by the speed of the wind. Doubling wind speed, increases wind erosion by a factor of eight. A key for erosion control is therefore controlling the speed of the wind over the surface.

Fabric

Fabrics are meshes made from high density polyethylene or polypropylene yarns. They are inter-locked by knitting or weaving into specified patterns. The nature of the mesh construction determines the structural strength and other properties of the fabric.

Fabric Panels

Panels cut and sewn to preset sizes together with a reinforced hem for transferring the load to the main cables and the poles.

Fire-rated

Fog

A very fine mist of water, with droplets small enough to join with fine dust particles.

Layout

The pattern of the windbreak fences on the orchard or other area being sheltered. The pattern is chosen to maximise the effectiveness of the windbreak at slowing winds. It is primarily influenced by the height and aerodynamic porosity of the windbreaks and by the topography of the area.

Light Spectrum

The colour of the fabric influences the colour (or spectrum) of the light that is absorbed, and hence the spectrum seen by the plants. Black fabrics absorb all light equally. White and “clear” fabrics have a reduced effect on the ultra-violets, but a similar effect to black on the infra-reds.

Nets

Any fabric made in a honeycomb pattern.

Ramp

When wind hits a vertical barrier it is thrown vertically. An inclined barrier throws the wind up at an angle. This more gradual process gives a longer flatter protected area behind the windbreak.

Retractable Anchor System

Screw anchors installed and removed with a power-auger that fit into slots in the concrete base.

Security Mesh

Steel diamond mesh supported with highly tensioned steel cables to hold the mesh up and square.

Shade Levels

Shade is the opposite of porosity. 100% shade is solid. Shade levels under coloured and white fabrics are measured in PAR (photsynthetically active radiation). This is approximately equivalent to visible radiation. A white fabric will typically have a shade level of about 7/10 of that of a black fabric of the same construction.

Sheltered Zone

The lee zone of the windbreak. The level of sheltering depends on the aerodynamic porosity of the windbreak, the local topography, the height and the angle of the windbreak to the wind. In addition, the shelter becomes less with distance away from the windbreak.

Suspension System

A support strucure comprising a “drooped” main cable running across a block and supporting several rows of fabric. The maximum economic span of the suspension system depends on the porosity of the fabric being supported. Distances of 150ft to 500ft (50m to 150m) are typical.

Wind Force

Wind force = windspeed x windspeed So, when windspeed is 1/4, wind force is 1/4 x 1/4 = 1/16 Wind force is what you feel when you try to stand up in a strong wind. Wind force is what blows the dust, bends the tree branch and so on.

Wind Protection Benefits

Click here to see a graph showing environmental changes behind a typical windbreak. Environments Inc designers can design a windbreak to considerably exceed these levels of protection if required.

Wind-Loads

The pressure on the fabric caused by winds of different speeds.

Woven Fabric

Fabric formed by inter-weaving straight yarns. Leno weave has pairs of yarns in the long direction that are effectively twisted together for additional stability.

Aerodynamic Porosity

The ratio of holes to solid that the wind “sees”. Aerodynamic porosity is less than visual porosity, by an amount that depends on the construction of the holes.

“Break-away” Clipping

Stress-rated nylon clips connecting the fabric to the main cables. The clips are spaced along the cable according to the wind load to which the structure has been designed.